Thursday, May 16, 2013

New paper suggests cosmic rays trigger lightning strikes

Cosmic rays are thought to have significant effects upon climate by increasing cloud formation and acting as amplifiers of solar activity [Svensmark's theory of cosmoclimatology]. A new paper may finally solve the mystery of what triggers lightening, finding cosmic rays interacting with water droplets within thunderclouds could play an important role in initiating lightning strikes. If confirmed, the finding could represent another mechanism by which tiny changes in solar activity can have amplified effects upon climate and weather via cosmic rays.

Cosmic rays interacting with water droplets within thunderclouds could play an important role in initiating lightning strikes. That is the claim of researchers in Russia, who have studied the radio signals emitted during thousands of lightning strikes. The work could provide new insights into how and why lightning occurs in the first place.

Although most people have witnessed a flash of lightning during a thunderstorm at some point in their lives, scientists still do not completely understand what triggers the discharge in the first place. Lightning has been studied for hundreds of years, yet while many possibilities for observation are available – there are about 40 to 50 lightning strikes per second across the globe – predicting the onset of a strike is difficult.

There are three basic types of lightning: lightning that occurs within a single cloud; lightning that occurs between two clouds; and lightning that occurs between a cloud and the Earth's surface. In a typical cloud-to-ground lightning strike, scientists know that an electrically-conducting plasma channel forms between the cloud and the ground, which allows the discharge to occur. However, the factors that cause the initial charging of the cloud and its subsequent discharge are not clearly understood.

Cosmic ray kick-off

Now, Aleksandr Gurevich of the Lebedev Physical Institute in Moscow and Anatoly Karashtin of the Radiophysical Research Institute in Nizhny Novgorod have suggested a new model that includes two crucial factors that could help explain the process: the behaviour of water or ice particles inside clouds, dubbed "hydrometeors"; and showers of ionized electrons that might be created by cosmic rays.

The theory that cosmic rays may cause the ionized showers that initiate lightning was first put forward by Gurevich more than 20 years ago. Known as "runaway breakdown", Gurevich suggested that the ionized particles create free electrons within thunderclouds that are then accelerated to extremely high energies by electric fields within the clouds. These electrons collide with other atoms in the air to cause an "avalanche" of high-energy particles within the cloud – and this provides the seed for the onset of lightning. While the theory was widely discussed, Gurevich was not able to find proof that cosmic rays do indeed trigger the avalanche.

In a bid to gather more evidence, Gurevich and Karashtin have now done a new analysis using a radio interferometer of radio pulses emitted at the onset of 3800 lightning strikes across Russia and Kazakhstan. A long series of these short yet strong pulses is emitted just before lightning strikes and, according the researchers, the pulse data match Gurevich's model of electrical breakdown.

Pulses of information

The researchers also point out that the amplitude of a pulse is proportional to the number of secondary electrons, and so also to the energy of the initial cosmic ray that generates the shower. But when they calculated the cosmic-ray energy, Gurevich and Karashtin found it to be about 1017 eV – a surprising figure as cosmic rays of this energy are too rare to explain what was measured.

To explain why such high energies were observed, the researchers suggest that the hydrometeors they used become electrically polarized as the strong electric field inside the cloud builds up and that a further "micro-discharge" occurs at the hydrometeor as the field reaches its threshold, thereby effectively amplifying the cosmic-ray-initiated breakdown. When this is taken into consideration, then much more common cosmic-ray particles with energies of about 1012–1013 eV are sufficient to initialize a discharge.

Physicist and lightning expert Joseph Dwyer of the Florida Institute of Technology, who was not involved in the current research, said that the new model is "an interesting idea, but much more work is still needed, for example experiments to measure radio pulses and air showers at the same time", which is something that Dwyer and his colleagues are currently working on themselves.

Gurevich and Karashtin said that their observations show that the radio emissions are generated by the specific discharges in thunderclouds, which are different from the conventional electric discharges expected and that the “runaway breakdown” plays a significant role too. Further observations will be necessary to finally crack the mystery of the atmospheric crackle.

5 comments:

Firstly, this paper has precisely nothing to do with climate. It proposes a mechanism for the formation and discharge of enormous electrical charge in thunderclouds; that is all. Its authors would not claim any connection between these electrical effects seen in clouds and the climate as a whole.

Secondly, another far more significant paper was published this week in the journal Meteorology and Atmospheric Physics. Unlike this one it actually investigates the relationship between cosmic rays and climate. It’s the results of the very experiment originally proposed by Henrik Svensmark. And guess what? It says there is no connection. This is the abstract of that paper:

“Our analysis shows that, although important in cloud physics the results do not lead to the conclusion that cosmic rays affect atmospheric clouds significantly, at least if H2SO4 is the dominant source of aerosols in the atmosphere. An analysis of the very recent studies of stratospheric aerosol changes following a giant solar energetic particles event shows a similar negligible effect. Recent measurements of the cosmic ray intensity show that a former decrease with time has been reversed. Thus, even if cosmic rays enhanced cloud production, there would be a small global cooling, not warming.”

More here: http://link.springer.com/article/10.1007%2Fs00703-013-0260-x

1. I'm well aware this particular paper says nothing about climate, but it does about the weather phenomenon lightening, and that is why I stated "...effects upon climate and weather via cosmic rays"

>>>My point exactly. The word "climate" has no place in that sentence. It's nothing to do with climate and therefore irrelevant to this blog, never mind this post.

2. One paper does not make a "consensus," even though I object to use of that term in science. There are many others that have found significant cloud effects from cosmic rays.

>>> Who used the word consensus? Not me. I merely pointed out that you cited a paper entirely irrelevant to the subject of your blog as supporting evidence while ignoring one which flatly contradicts your thesis.

3. "Thus, even if cosmic rays enhanced cloud production, there would be a small global cooling, not warming.” Yes, of course! That is the whole basis of Svensmark's theory:

Weak Sun > more cosmic rays > more clouds > more cooling

and vice versa! The Sun peaked at the highest activity of the past 10,000 years at the end of the 20th century > fewer clouds > more warming!

>>> Do you know what cosmic rays actually are? A tiny proportion of them have their origins in the solar wind. Most of them, and all of those with greater energies, ie the most ionising, have an origin outside our Solar System. You're not convincing me you have much grasp of basic science.

1. I'll post whatever is of interest to me on my own blog. Not all posts concern climate, some concern weather, some concern politics, etc. This paper is of interest to me for the following reasons, not that I have to justify my interest in topics to you or anyone else.

a. We still don't understand what triggers lightning, one of hundreds of aspects of atmospheric science still not understood, despite all the claims of "settled science."b. The more we know, the more we don't know, such as all the effects of cosmic rays on the atmosphere, including WEATHER and CLIMATE.c. Solar activity controls, via the solar wind, how many cosmic rays reach the Earth. If cosmic ray activity affects lightning activity, then the Sun indirectly affects lightning activity.

2. You cited one paper as if that overturns all of Svensmark's theory. It does not.